The use of collagen and modified collagen gels for soft contact lens has been described in the art. See for example, U.S. Pat. No. 4,223,984 to Miyata et al and U.S. Pat. No. 4,260,228 to Miyata wherein methods for removing collagen from calfskin and preparing collagen gels for use in soft contact lenses are described. Heretofore, however, a problem presented by such collagen lenses was eye irritation which apparently results from the presence of pyrogens in the collagen gel lens.
It has now been discovered that a pyrogen-free, collagen gel is essential for use in collagen gel contact lenses, particularly when such lenses are intended for extended wear. If the collagen gel is not highly purified and is not pyrogen-free, the lens manufactured from it is irritating to the eyes, causing redness, follicular response, and mucus discharge. Collagen gels which contain pyrogens have heretofore resisted all efforts to render them pyrogen-free after manufacture through treatment with various sterilizing agents. It has now, however, been surprisingly determined that a pyrogen-free condition can be achieved provided each individual process step is carried out in an aseptic manner.